"There are albums, usually the first from a particular artist, that capture their signature sound only just beginning to take shape. They occupy a unique moment in time, being less certain of their identity and direction. While this makes them appear less essential for fans who are already accustomed to the artist’s most defining works, they also continue to stand apart as a reminder of their stylistic beginnings, perhaps foreshadowing the direction they were to head in. Slayer’s debut album Show No Mercy is one of the most recognisable examples of this within metal as a whole, and for good reason. While the standard-tuned guitars, melodic solos and riffs, and upbeat but not extreme tempos situate the album firmly within the speed and thrash metal styles rapidly gaining prominence in 1983, beneath its sound is a dark, distinctly Satanic-themed underbelly that hints at the band’s ultimate aspirations."

- King_of_Arnor, metal-archives.com